```
@Retention(RUNTIME)
@Target(TYPE)
@Documented
public @interface JsFunction
```
JsFunction marks a functional interface as being the definition of a JavaScript function.
There are some limitations exists on JsFunction to make them practical and efficient:
- A JsFunction interface cannot extend any other interfaces.
- A class may not implement more than one JsFunction interface.
- A class that implements a JsFunction type cannot be a JsType (directly or indirectly).
- Fields and defender methods of the interfaces should be marked with JsOverlay and cannot be overridden by the implementations.
As a best practice, we also recommend marking JsFunction interfaces with FunctionalInterface to get improved checking in IDEs.
Instanceof and Castability:
Instanceof and casting for JsFunction is effectively a JavaScript typeof check to determine if the instance is a function.

Annotation Type JsFunction